docs: improve language in root files (#2894)

I asked Gemini to review the English for inconsistencies and grammar
mistakes. This is the result and I hope it's useful!

As a non-native speaker, it is hard for me to evaluate the finer
details, so let me know if you would like to see changes (or even
better: make them directly in the PR with the suggestion function).

src/index.md

@@ -32,7 +32,7 @@ Building on this, you're invited to dive into one or more specialized topics:
 
 - [Android](android.md): a half-day course on using Rust for Android platform
   development (AOSP). This includes interoperability with C, C++, and Java.
-- [Chromium](chromium.md): a half-day course on using Rust within Chromium based
+- [Chromium](chromium.md): a half-day course on using Rust in Chromium-based
   browsers. This includes interoperability with C++ and how to include
   third-party crates in Chromium.
 - [Bare-metal](bare-metal.md): a whole-day class on using Rust for bare-metal

src/welcome-day-1.md

@@ -26,9 +26,10 @@ Please remind the students that:
 - They should ask questions when they get them, don't save them to the end.
 - The class is meant to be interactive and discussions are very much encouraged!
   - As an instructor, you should try to keep the discussions relevant, i.e.,
-    keep the discussions related to how Rust does things vs some other language.
-    It can be hard to find the right balance, but err on the side of allowing
-    discussions since they engage people much more than one-way communication.
+    keep the discussions related to how Rust does things vs. some other
+    language. It can be hard to find the right balance, but err on the side of
+    allowing discussions since they engage people much more than one-way
+    communication.
 - The questions will likely mean that we talk about things ahead of the slides.
   - This is perfectly okay! Repetition is an important part of learning.
     Remember that the slides are just a support and you are free to skip them as